1. Field of the Invention
The present invention relates to an internal combustion engine with a by-pass control system.
2. Description of the Related Art
In an internal combustion engine provided with a mechanical supercharging system, a Roots blower is connected as a supercharger to an engine crankshaft by way of a clutch. The clutch is engaged or disengaged in accordance with the engine load, engine speed, and other engine conditions. The clutch is engaged when the engine load is high to obtain a high engine torque. Furthermore, the clutch is engaged at a predetermined engine speed in order to prevent possible shock or damage to the clutch arising from engagement at higher engine speeds.
In one known supercharging device with a clutch, a by-pass is provided. A by-pass control valve is arranged in the by-pass to allow operation in accordance with engine load (see Japanese Unexamined Patent Publication (Kokai) No. 56-167817). The by-pass control valve is used to control the amount of supercharging air during the supercharging state of the engine where the clutch is engaged. When the engine load is high, the by-pass control valve is closed, so that no diversion of air into the by-pass occurs and the pressure of air into the engine become high, thus enabling high engine output. When the engine load becomes small, the by-pass control valve is opened. The air from the supercharger is thus diverted to the by-pass, and the pressure of air into the engine decreases. This decreases the effort required for attaining compression in the supercharger and increases fuel consumption efficiency.
In this prior art system, however, the control of the supercharger by the clutch and the control of the by-pass are independent. Therefore, there is an area where the clutch is changed from disengaged to engaged state while the by-pass is maintained open. In this case, there is a certain delay in the increase in speed of the supercharger after the clutch engagement due to the relatively low speed of the supercharger, caused by the small amount of air passing through the supercharger, just before the clutch engagement. The delay makes the engine torque become small. Note that there is a tendency toward the temporary decrease in torque when the clutch is engaged due to the inertia effect. The drop is amplified by the opened state of the by-pass.